/**
 * @file
 * Packet buffer management
 *
 * Packets are built from the pbuf data structure. It supports dynamic
 * memory allocation for packet contents or can reference externally
 * managed packet contents both in RAM and ROM. Quick allocation for
 * incoming packets is provided through pools with fixed sized pbufs.
 *
 * A packet may span over multiple pbufs, chained as a singly linked
 * list. This is called a "pbuf chain".
 *
 * Multiple packets may be queued, also using this singly linked list.
 * This is called a "packet queue".
 *
 * So, a packet queue consists of one or more pbuf chains, each of
 * which consist of one or more pbufs. Currently, queues are only
 * supported in a limited section of lwIP, this is the etharp queueing
 * code. Outside of this section no packet queues are supported yet.
 *
 * The differences between a pbuf chain and a packet queue are very
 * precise but subtle.
 *
 * The last pbuf of a packet has a ->tot_len field that equals the
 * ->len field. It can be found by traversing the list. If the last
 * pbuf of a packet has a ->next field other than NULL, more packets
 * are on the queue.
 *
 * Therefore, looping through a pbuf of a single packet, has an
 * loop end condition (tot_len == p->len), NOT (next == NULL).
 */

/*
 * Copyright (c) 2001-2004 Swedish Institute of Computer Science.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modification,
 * are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 * 3. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT
 * SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
 * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
 * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY
 * OF SUCH DAMAGE.
 *
 * This file is part of the lwIP TCP/IP stack.
 *
 * Author: Adam Dunkels <adam@sics.se>
 *
 */

#include <string.h>

#include "lwip/opt.h"
#include "lwip/stats.h"
#include "lwip/def.h"
#include "lwip/mem.h"
#include "lwip/memp.h"
#include "lwip/pbuf.h"
#include "lwip/sys.h"
#include "arch/perf.h"

//static u8_t pbuf_pool_memory[MEM_ALIGNMENT - 1 + PBUF_POOL_SIZE * MEM_ALIGN_SIZE(PBUF_POOL_BUFSIZE + sizeof(struct pbuf))];

#if !SYS_LIGHTWEIGHT_PROT
static volatile u8_t pbuf_pool_free_lock, pbuf_pool_alloc_lock;
static sys_sem_t pbuf_pool_free_sem;
#endif

static struct pbuf *pbuf_pool = NULL;

/**
 * Initializes the pbuf module.
 *
 * A large part of memory is allocated for holding the pool of pbufs.
 * The size of the individual pbufs in the pool is given by the size
 * parameter, and the number of pbufs in the pool by the num parameter.
 *
 * After the memory has been allocated, the pbufs are set up. The
 * ->next pointer in each pbuf is set up to point to the next pbuf in
 * the pool.
 *
 */
void pbuf_init(void)
{
        struct pbuf *p, *q = NULL;
        u16_t i;

        pbuf_pool = (struct pbuf *)mem_malloc(PBUF_POOL_BUFSIZE + sizeof(struct pbuf));
        LWIP_ASSERT("NOT enough memory for pbuf_init!!!\n", (pbuf_pool != NULL));

#if PBUF_STATS
        lwip_stats.pbuf.avail = PBUF_POOL_SIZE;
#endif /* PBUF_STATS */

        /* Set up ->next pointers to link the pbufs of the pool together */
        p = pbuf_pool;

        for (i = 0; i < PBUF_POOL_SIZE - 1; ++i) {
                p->next = (struct pbuf *)mem_malloc(PBUF_POOL_BUFSIZE + sizeof(struct pbuf));
                LWIP_ASSERT("NOT enough memory for pbuf_init!!!\n", (p->next != NULL));
                p->len = p->tot_len = PBUF_POOL_BUFSIZE;
                p->payload = (void *)((u8_t *)p + sizeof(struct pbuf));
                p->flags = PBUF_FLAG_POOL;
                q = p;
                p = p->next;
        }
        /* last buffer */
        p->next = NULL;
        p->len = p->tot_len = PBUF_POOL_BUFSIZE;
        p->payload = (void *)((u8_t *)p + sizeof(struct pbuf));
        p->flags = PBUF_FLAG_POOL;


#if !SYS_LIGHTWEIGHT_PROT
        pbuf_pool_alloc_lock = 0;
        pbuf_pool_free_lock = 0;
        pbuf_pool_free_sem = sys_sem_new(1);
#endif
}

/**
 * @internal only called from pbuf_alloc()
 */
static struct pbuf *pbuf_pool_alloc(void)
{
        struct pbuf *p = NULL;

        SYS_ARCH_DECL_PROTECT(old_level);
        SYS_ARCH_PROTECT(old_level);

#if !SYS_LIGHTWEIGHT_PROT
        /* Next, check the actual pbuf pool, but if the pool is locked, we
           pretend to be out of buffers and return NULL. */
        if (pbuf_pool_free_lock)
        {
#if PBUF_STATS
                ++lwip_stats.pbuf.alloc_locked;
#endif /* PBUF_STATS */
                return NULL;
        }
        pbuf_pool_alloc_lock = 1;
        if (!pbuf_pool_free_lock)
        {
#endif /* SYS_LIGHTWEIGHT_PROT */
                p = pbuf_pool;
                if (p) {
                        pbuf_pool = p->next;
                }
#if !SYS_LIGHTWEIGHT_PROT
#if PBUF_STATS
        } else
        {
                ++lwip_stats.pbuf.alloc_locked;
#endif /* PBUF_STATS */
        }
        pbuf_pool_alloc_lock = 0;
#endif /* SYS_LIGHTWEIGHT_PROT */

#if PBUF_STATS
        if (p != NULL)
        {
                ++lwip_stats.pbuf.used;
                if (lwip_stats.pbuf.used > lwip_stats.pbuf.max) {
                        lwip_stats.pbuf.max = lwip_stats.pbuf.used;
                }
        }
#endif /* PBUF_STATS */

        SYS_ARCH_UNPROTECT(old_level);
        return p;
}


/**
 * Allocates a pbuf of the given type (possibly a chain for PBUF_POOL type).
 *
 * The actual memory allocated for the pbuf is determined by the
 * layer at which the pbuf is allocated and the requested size
 * (from the size parameter).
 *
 * @param flag this parameter decides how and where the pbuf
 * should be allocated as follows:
 *
 * - PBUF_RAM: buffer memory for pbuf is allocated as one large
 *             chunk. This includes protocol headers as well.
 * - PBUF_ROM: no buffer memory is allocated for the pbuf, even for
 *             protocol headers. Additional headers must be prepended
 *             by allocating another pbuf and chain in to the front of
 *             the ROM pbuf. It is assumed that the memory used is really
 *             similar to ROM in that it is immutable and will not be
 *             changed. Memory which is dynamic should generally not
 *             be attached to PBUF_ROM pbufs. Use PBUF_REF instead.
 * - PBUF_REF: no buffer memory is allocated for the pbuf, even for
 *             protocol headers. It is assumed that the pbuf is only
 *             being used in a single thread. If the pbuf gets queued,
 *             then pbuf_take should be called to copy the buffer.
 * - PBUF_POOL: the pbuf is allocated as a pbuf chain, with pbufs from
 *              the pbuf pool that is allocated during pbuf_init().
 *
 * @return the allocated pbuf. If multiple pbufs where allocated, this
 * is the first pbuf of a pbuf chain.
 */
struct pbuf *pbuf_alloc(pbuf_layer l, u16_t length, pbuf_flag flag)
{
        struct pbuf *p, *q, *r;
        u16_t offset;
        s32_t rem_len; /* remaining length */
        LWIP_DEBUGF(PBUF_DEBUG | DBG_TRACE | 3, ("pbuf_alloc(length=%"U16_F")\n", length));

        /* determine header offset */
        offset = 0;
        switch (l)
        {
        case PBUF_TRANSPORT:
                /* add room for transport (often TCP) layer header */
                offset += PBUF_TRANSPORT_HLEN;
                /* FALLTHROUGH */
        case PBUF_IP:
                /* add room for IP layer header */
                offset += PBUF_IP_HLEN;
                /* FALLTHROUGH */
        case PBUF_LINK:
                /* add room for link layer header */
                offset += PBUF_LINK_HLEN;
                break;
        case PBUF_RAW:
                break;
        default:
                LWIP_ASSERT("pbuf_alloc: bad pbuf layer", 0);
                return NULL;
        }

        switch (flag)
        {
        case PBUF_POOL:
                /* allocate head of pbuf chain into p */
                p = pbuf_pool_alloc();
                LWIP_DEBUGF(PBUF_DEBUG | DBG_TRACE | 3, ("pbuf_alloc: allocated pbuf %x\n", (unsigned int)p));
                if (p == NULL) {
#if PBUF_STATS
                        ++lwip_stats.pbuf.err;
#endif /* PBUF_STATS */
                        return NULL;
                }
                p->next = NULL;

                /* make the payload pointer point 'offset' bytes into pbuf data memory */
                p->payload = (void *)((u8_t *)p + (sizeof(struct pbuf) + offset));
                LWIP_ASSERT("pbuf_alloc: pbuf p->payload properly aligned",
                            ((mem_ptr_t)p->payload % MEM_ALIGNMENT) == 0);
                /* the total length of the pbuf chain is the requested size */
                p->tot_len = length;
                /* set the length of the first pbuf in the chain */
                p->len = length > PBUF_POOL_BUFSIZE - offset? PBUF_POOL_BUFSIZE - offset: length;
                /* set reference count (needed here in case we fail) */
                p->ref = 1;

                /* now allocate the tail of the pbuf chain */

                /* remember first pbuf for linkage in next iteration */
                r = p;
                /* remaining length to be allocated */
                rem_len = length - p->len;
                /* any remaining pbufs to be allocated? */
                while (rem_len > 0) {
                        q = pbuf_pool_alloc();
                        if (q == NULL) {
                                LWIP_DEBUGF(PBUF_DEBUG | 2, ("pbuf_alloc: Out of pbufs in pool.\n"));
#if PBUF_STATS
                                ++lwip_stats.pbuf.err;
#endif /* PBUF_STATS */
                                /* free chain so far allocated */
                                pbuf_free(p);
                                /* bail out unsuccesfully */
                                return NULL;
                        }
                        q->next = NULL;
                        /* make previous pbuf point to this pbuf */
                        r->next = q;
                        /* set total length of this pbuf and next in chain */
                        q->tot_len = rem_len;
                        /* this pbuf length is pool size, unless smaller sized tail */
                        q->len = rem_len > PBUF_POOL_BUFSIZE? PBUF_POOL_BUFSIZE: rem_len;
                        q->payload = (void *)((u8_t *)q + sizeof(struct pbuf));
                        LWIP_ASSERT("pbuf_alloc: pbuf q->payload properly aligned",
                                    ((mem_ptr_t)q->payload % MEM_ALIGNMENT) == 0);
                        q->ref = 1;
                        /* calculate remaining length to be allocated */
                        rem_len -= q->len;
                        /* remember this pbuf for linkage in next iteration */
                        r = q;
                }
                /* end of chain */
                /*r->next = NULL;*/

                break;
        case PBUF_RAM:
                /* If pbuf is to be allocated in RAM, allocate memory for it. */
                p = mem_malloc(MEM_ALIGN_SIZE(sizeof(struct pbuf) + offset) + MEM_ALIGN_SIZE(length));
                if (p == NULL) {
                        return NULL;
                }
                /* Set up internal structure of the pbuf. */
                p->payload = (void *)((u8_t *)p + sizeof(struct pbuf) + offset);
                p->len = p->tot_len = length;
                p->next = NULL;
                p->flags = PBUF_FLAG_RAM;

                LWIP_ASSERT("pbuf_alloc: pbuf->payload properly aligned",
                            ((mem_ptr_t)p->payload % MEM_ALIGNMENT) == 0);
                break;
                /* pbuf references existing (non-volatile static constant) ROM payload? */
        case PBUF_ROM:
                /* pbuf references existing (externally allocated) RAM payload? */
        case PBUF_REF:
                /* only allocate memory for the pbuf structure */
                p = memp_malloc(MEMP_PBUF);
                if (p == NULL) {
                        LWIP_DEBUGF(PBUF_DEBUG | DBG_TRACE | 2, ("pbuf_alloc: Could not allocate MEMP_PBUF for PBUF_%s.\n", flag == PBUF_ROM?"ROM":"REF"));
                        return NULL;
                }
                /* caller must set this field properly, afterwards */
                p->payload = NULL;
                p->len = p->tot_len = length;
                p->next = NULL;
                p->flags = (flag == PBUF_ROM? PBUF_FLAG_ROM: PBUF_FLAG_REF);
                break;
        default:
                LWIP_ASSERT("pbuf_alloc: erroneous flag", 0);
                return NULL;
        }
        /* set reference count */
        p->ref = 1;
        LWIP_DEBUGF(PBUF_DEBUG | DBG_TRACE | 3, ("pbuf_alloc(length=%"U16_F") == %x\n", length, (unsigned int)p));
        return p;
}


#if PBUF_STATS
#define DEC_PBUF_STATS do { --lwip_stats.pbuf.used; } while (0)
#else /* PBUF_STATS */
#define DEC_PBUF_STATS
#endif /* PBUF_STATS */

#define PBUF_POOL_FAST_FREE(p)  do {                                    \
                                  p->next = pbuf_pool;                  \
                                  pbuf_pool = p;                        \
                                  DEC_PBUF_STATS;                       \
                                } while (0)

#if SYS_LIGHTWEIGHT_PROT
#define PBUF_POOL_FREE(p)  do {                                         \
                                SYS_ARCH_DECL_PROTECT(old_level);       \
                                SYS_ARCH_PROTECT(old_level);            \
                                PBUF_POOL_FAST_FREE(p);                 \
                                SYS_ARCH_UNPROTECT(old_level);          \
                               } while (0)
#else /* SYS_LIGHTWEIGHT_PROT */
#define PBUF_POOL_FREE(p)  do {                                         \
                             sys_sem_wait(&pbuf_pool_free_sem);          \
                             PBUF_POOL_FAST_FREE(p);                    \
                             sys_sem_signal(&pbuf_pool_free_sem);        \
                           } while (0)
#endif /* SYS_LIGHTWEIGHT_PROT */

/**
 * Shrink a pbuf chain to a desired length.
 *
 * @param p pbuf to shrink.
 * @param new_len desired new length of pbuf chain
 *
 * Depending on the desired length, the first few pbufs in a chain might
 * be skipped and left unchanged. The new last pbuf in the chain will be
 * resized, and any remaining pbufs will be freed.
 *
 * @note If the pbuf is ROM/REF, only the ->tot_len and ->len fields are adjusted.
 * @note May not be called on a packet queue.
 *
 * @bug Cannot grow the size of a pbuf (chain) (yet).
 */
void pbuf_realloc(struct pbuf *p, u16_t new_len)
{
        struct pbuf *q;
        u16_t rem_len; /* remaining length */
        s16_t grow;

        LWIP_ASSERT("pbuf_realloc: sane p->flags", p->flags == PBUF_FLAG_POOL ||
                    p->flags == PBUF_FLAG_ROM ||
                    p->flags == PBUF_FLAG_RAM ||
                    p->flags == PBUF_FLAG_REF);

        /* desired length larger than current length? */
        if (new_len >= p->tot_len)
        {
                /* enlarging not yet supported */
                return;
        }

        /* the pbuf chain grows by (new_len - p->tot_len) bytes
         * (which may be negative in case of shrinking) */
        grow = new_len - p->tot_len;

        /* first, step over any pbufs that should remain in the chain */
        rem_len = new_len;
        q = p;
        /* should this pbuf be kept? */
        while (rem_len > q->len)
        {
                /* decrease remaining length by pbuf length */
                rem_len -= q->len;
                /* decrease total length indicator */
                q->tot_len += grow;
                /* proceed to next pbuf in chain */
                q = q->next;
        }
        /* we have now reached the new last pbuf (in q) */
        /* rem_len == desired length for pbuf q */

        /* shrink allocated memory for PBUF_RAM */
        /* (other types merely adjust their length fields */
        if ((q->flags == PBUF_FLAG_RAM) && (rem_len != q->len))
        {
                /* reallocate and adjust the length of the pbuf that will be split */
                mem_realloc(q, (u8_t *)q->payload - (u8_t *)q + rem_len);
        }
        /* adjust length fields for new last pbuf */
        q->len = rem_len;
        q->tot_len = q->len;

        /* any remaining pbufs in chain? */
        if (q->next != NULL)
        {
                /* free remaining pbufs in chain */
                pbuf_free(q->next);
        }
        /* q is last packet in chain */
        q->next = NULL;

}

/**
 * Adjusts the payload pointer to hide or reveal headers in the payload.
 *
 * Adjusts the ->payload pointer so that space for a header
 * (dis)appears in the pbuf payload.
 *
 * The ->payload, ->tot_len and ->len fields are adjusted.
 *
 * @param hdr_size_inc Number of bytes to increment header size which
 * increases the size of the pbuf. New space is on the front.
 * (Using a negative value decreases the header size.)
 * If hdr_size_inc is 0, this function does nothing and returns succesful.
 *
 * PBUF_ROM and PBUF_REF type buffers cannot have their sizes increased, so
 * the call will fail. A check is made that the increase in header size does
 * not move the payload pointer in front of the start of the buffer.
 * @return non-zero on failure, zero on success.
 *
 */
u8_t pbuf_header(struct pbuf *p, s16_t header_size_increment)
{
        void *payload;

        LWIP_ASSERT("p != NULL", p != NULL);
        if ((header_size_increment == 0) || (p == NULL)) return 0;

        /* remember current payload pointer */
        payload = p->payload;

        /* pbuf types containing payloads? */
        if (p->flags == PBUF_FLAG_RAM || p->flags == PBUF_FLAG_POOL)
        {
                /* set new payload pointer */
                p->payload = (u8_t *)p->payload - header_size_increment;
                /* boundary check fails? */
                if ((u8_t *)p->payload < (u8_t *)p + sizeof(struct pbuf)) {
                        LWIP_DEBUGF( PBUF_DEBUG | 2, ("pbuf_header: failed as %x < %x (not enough space for new header size)\n",
                                                      (unsigned int)p->payload,
                                                      (unsigned int)(p + 1)));
                        \
                        /* restore old payload pointer */
                        p->payload = payload;
                        /* bail out unsuccesfully */
                        return 1;
                }
                /* pbuf types refering to external payloads? */
        } else if (p->flags == PBUF_FLAG_REF || p->flags == PBUF_FLAG_ROM)
        {
                /* hide a header in the payload? */
                if ((header_size_increment < 0) && (header_size_increment - p->len <= 0)) {
                        /* increase payload pointer */
                        p->payload = (u8_t *)p->payload - header_size_increment;
                } else {
                        /* cannot expand payload to front (yet!)
                         * bail out unsuccesfully */
                        return 1;
                }
        }
        /* modify pbuf length fields */
        p->len += header_size_increment;
        p->tot_len += header_size_increment;

        LWIP_DEBUGF( PBUF_DEBUG, ("pbuf_header: old %x new %x (%"S16_F")\n",
                                  (unsigned int)payload, (unsigned int)p->payload, header_size_increment));

        return 0;
}

/**
 * Dereference a pbuf chain or queue and deallocate any no-longer-used
 * pbufs at the head of this chain or queue.
 *
 * Decrements the pbuf reference count. If it reaches zero, the pbuf is
 * deallocated.
 *
 * For a pbuf chain, this is repeated for each pbuf in the chain,
 * up to the first pbuf which has a non-zero reference count after
 * decrementing. So, when all reference counts are one, the whole
 * chain is free'd.
 *
 * @param pbuf The pbuf (chain) to be dereferenced.
 *
 * @return the number of pbufs that were de-allocated
 * from the head of the chain.
 *
 * @note MUST NOT be called on a packet queue (Not verified to work yet).
 * @note the reference counter of a pbuf equals the number of pointers
 * that refer to the pbuf (or into the pbuf).
 *
 * @internal examples:
 *
 * Assuming existing chains a->b->c with the following reference
 * counts, calling pbuf_free(a) results in:
 *
 * 1->2->3 becomes ...1->3
 * 3->3->3 becomes 2->3->3
 * 1->1->2 becomes ......1
 * 2->1->1 becomes 1->1->1
 * 1->1->1 becomes .......
 *
 */
u8_t pbuf_free(struct pbuf *p)
{
        struct pbuf *q;
        u8_t count;
        SYS_ARCH_DECL_PROTECT(old_level);


        LWIP_ASSERT("p != NULL", p != NULL);
        /* if assertions are disabled, proceed with debug output */
        if (p == NULL)
        {
                LWIP_DEBUGF(PBUF_DEBUG | DBG_TRACE | 2, ("pbuf_free(p == NULL) was called.\n"));
                return 0;
        }
        LWIP_DEBUGF(PBUF_DEBUG | DBG_TRACE | 3, ("pbuf_free(%x)\n", (unsigned int)p));

        PERF_START;

        LWIP_ASSERT("pbuf_free: sane flags",
                    p->flags == PBUF_FLAG_RAM || p->flags == PBUF_FLAG_ROM ||
                    p->flags == PBUF_FLAG_REF || p->flags == PBUF_FLAG_POOL);



        count = 0;
        /* Since decrementing ref cannot be guaranteed to be a single machine operation
         * we must protect it. Also, the later test of ref must be protected.
         */
        SYS_ARCH_PROTECT(old_level);
        /* de-allocate all consecutive pbufs from the head of the chain that
         * obtain a zero reference count after decrementing*/
        while (p != NULL)
        {
                /* all pbufs in a chain are referenced at least once */
                LWIP_ASSERT("pbuf_free: p->ref > 0", p->ref > 0);
                /* decrease reference count (number of pointers to pbuf) */
                p->ref--;
                /* this pbuf is no longer referenced to? */
                if (p->ref == 0) {
                        /* remember next pbuf in chain for next iteration */
                        q = p->next;
                        LWIP_DEBUGF( PBUF_DEBUG | 2, ("pbuf_free: deallocating %x\n", (unsigned int)p));
                        /* is this a pbuf from the pool? */
                        if (p->flags == PBUF_FLAG_POOL) {
                                p->len = p->tot_len = PBUF_POOL_BUFSIZE;
                                p->payload = (void *)((u8_t *)p + sizeof(struct pbuf));
                                PBUF_POOL_FREE(p);
                                /* is this a ROM or RAM referencing pbuf? */
                        } else if (p->flags == PBUF_FLAG_ROM || p->flags == PBUF_FLAG_REF) {
                                memp_free(MEMP_PBUF, p);
                                /* p->flags == PBUF_FLAG_RAM */
                        } else {
                                mem_free(p);
                        }
                        count++;
                        /* proceed to next pbuf */
                        p = q;
                        /* p->ref > 0, this pbuf is still referenced to */
                        /* (and so the remaining pbufs in chain as well) */
                } else {
                        LWIP_DEBUGF( PBUF_DEBUG | 2, ("pbuf_free: %x has ref %"U16_F", ending here.\n", (unsigned int)p, (u16_t)p->ref));
                        /* stop walking through the chain */
                        p = NULL;
                }
        }
        SYS_ARCH_UNPROTECT(old_level);
        PERF_STOP("pbuf_free");
        /* return number of de-allocated pbufs */
        return count;
}

/**
 * Count number of pbufs in a chain
 *
 * @param p first pbuf of chain
 * @return the number of pbufs in a chain
 */

u8_t pbuf_clen(struct pbuf *p)
{
        u8_t len;

        len = 0;
        while (p != NULL)
        {
                ++len;
                p = p->next;
        }
        return len;
}

/**
 * Increment the reference count of the pbuf.
 *
 * @param p pbuf to increase reference counter of
 *
 */
void pbuf_ref(struct pbuf *p)
{
        SYS_ARCH_DECL_PROTECT(old_level);
        /* pbuf given? */
        if (p != NULL)
        {
                SYS_ARCH_PROTECT(old_level);
                ++(p->ref);
                SYS_ARCH_UNPROTECT(old_level);
        }
}

/**
 * Concatenate two pbufs (each may be a pbuf chain) and take over
 * the caller's reference of the tail pbuf.
 *
 * @note The caller MAY NOT reference the tail pbuf afterwards.
 * Use pbuf_chain() for that purpose.
 *
 * @see pbuf_chain()
 */

void pbuf_cat(struct pbuf *h, struct pbuf *t)
{
        struct pbuf *p;

        LWIP_ASSERT("h != NULL (programmer violates API)", h != NULL);
        LWIP_ASSERT("t != NULL (programmer violates API)", t != NULL);
        if ((h == NULL) || (t == NULL)) return;

        /* proceed to last pbuf of chain */
        for (p = h; p->next != NULL; p = p->next)
        {
                /* add total length of second chain to all totals of first chain */
                p->tot_len += t->tot_len;
        }
        /* { p is last pbuf of first h chain, p->next == NULL } */
        LWIP_ASSERT("p->tot_len == p->len (of last pbuf in chain)", p->tot_len == p->len);
        LWIP_ASSERT("p->next == NULL", p->next == NULL);
        /* add total length of second chain to last pbuf total of first chain */
        p->tot_len += t->tot_len;
        /* chain last pbuf of head (p) with first of tail (t) */
        p->next = t;
        /* p->next now references t, but the caller will drop its reference to t,
         * so netto there is no change to the reference count of t.
         */
}

/**
 * Chain two pbufs (or pbuf chains) together.
 *
 * The caller MUST call pbuf_free(t) once it has stopped
 * using it. Use pbuf_cat() instead if you no longer use t.
 *
 * @param h head pbuf (chain)
 * @param t tail pbuf (chain)
 * @note The pbufs MUST belong to the same packet.
 * @note MAY NOT be called on a packet queue.
 *
 * The ->tot_len fields of all pbufs of the head chain are adjusted.
 * The ->next field of the last pbuf of the head chain is adjusted.
 * The ->ref field of the first pbuf of the tail chain is adjusted.
 *
 */
void pbuf_chain(struct pbuf *h, struct pbuf *t)
{
        pbuf_cat(h, t);
        /* t is now referenced by h */
        pbuf_ref(t);
        LWIP_DEBUGF(PBUF_DEBUG | DBG_FRESH | 2, ("pbuf_chain: %x references %x\n", (unsigned int)h, (unsigned int)t));
}

/* For packet queueing. Note that queued packets MUST be dequeued first
 * using pbuf_dequeue() before calling other pbuf_() functions. */
#if ARP_QUEUEING
/**
 * Add a packet to the end of a queue.
 *
 * @param q pointer to first packet on the queue
 * @param n packet to be queued
 *
 * Both packets MUST be given, and must be different.
 */
void pbuf_queue(struct pbuf *p, struct pbuf *n)
{
#if PBUF_DEBUG /* remember head of queue */
        struct pbuf *q = p;
#endif
        /* programmer stupidity checks */
        LWIP_ASSERT("p == NULL in pbuf_queue: this indicates a programmer error\n", p != NULL);
        LWIP_ASSERT("n == NULL in pbuf_queue: this indicates a programmer error\n", n != NULL);
        LWIP_ASSERT("p == n in pbuf_queue: this indicates a programmer error\n", p != n);
        if ((p == NULL) || (n == NULL) || (p == n))
        {
                LWIP_DEBUGF(PBUF_DEBUG | DBG_HALT | 3, ("pbuf_queue: programmer argument error\n"));
                return;
        }

        /* iterate through all packets on queue */
        while (p->next != NULL)
        {
                /* be very picky about pbuf chain correctness */
#if PBUF_DEBUG
                /* iterate through all pbufs in packet */
                while (p->tot_len != p->len) {
                        /* make sure invariant condition holds */
                        LWIP_ASSERT("p->len < p->tot_len", p->len < p->tot_len);
                        /* make sure each packet is complete */
                        LWIP_ASSERT("p->next != NULL", p->next != NULL);
                        p = p->next;
                        /* { p->tot_len == p->len => p is last pbuf of a packet } */
                }
                /* { p is last pbuf of a packet } */
                /* proceed to next packet on queue */
#endif
                /* proceed to next pbuf */
                if (p->next != NULL) p = p->next;
        }
        /* { p->tot_len == p->len and p->next == NULL } ==>
         * { p is last pbuf of last packet on queue } */
        /* chain last pbuf of queue with n */
        p->next = n;
        /* n is now referenced to by the (packet p in the) queue */
        pbuf_ref(n);
#if PBUF_DEBUG
        LWIP_DEBUGF(PBUF_DEBUG | DBG_FRESH | 2,
                    ("pbuf_queue: newly queued packet %x sits after packet %x in queue %x\n",
                     (unsigned int)n, (unsigned int)p, (unsigned int)q));
#endif
}

/**
 * Remove a packet from the head of a queue.
 *
 * The caller MUST reference the remainder of the queue (as returned). The
 * caller MUST NOT call pbuf_ref() as it implicitly takes over the reference
 * from p.
 *
 * @param p pointer to first packet on the queue which will be dequeued.
 * @return first packet on the remaining queue (NULL if no further packets).
 *
 */
struct pbuf *pbuf_dequeue(struct pbuf *p)
{
        struct pbuf *q;
        LWIP_ASSERT("p != NULL", p != NULL);

        /* iterate through all pbufs in packet p */
        while (p->tot_len != p->len)
        {
                /* make sure invariant condition holds */
                LWIP_ASSERT("p->len < p->tot_len", p->len < p->tot_len);
                /* make sure each packet is complete */
                LWIP_ASSERT("p->next != NULL", p->next != NULL);
                p = p->next;
        }
        /* { p->tot_len == p->len } => p is the last pbuf of the first packet */
        /* remember next packet on queue in q */
        q = p->next;
        /* dequeue packet p from queue */
        p->next = NULL;
        /* any next packet on queue? */
        if (q != NULL)
        {
                /* although q is no longer referenced by p, it MUST be referenced by
                 * the caller, who is maintaining this packet queue. So, we do not call
                 * pbuf_free(q) here, resulting in an implicit pbuf_ref(q) for the caller. */
                LWIP_DEBUGF(PBUF_DEBUG | DBG_FRESH | 2, ("pbuf_dequeue: first remaining packet on queue is %x\n", (unsigned int)q));
        } else
        {
                LWIP_DEBUGF(PBUF_DEBUG | DBG_FRESH | 2, ("pbuf_dequeue: no further packets on queue\n"));
        }
        return q;
}
#endif

/**
 *
 * Create PBUF_POOL (or PBUF_RAM) copies of PBUF_REF pbufs.
 *
 * Used to queue packets on behalf of the lwIP stack, such as
 * ARP based queueing.
 *
 * Go through a pbuf chain and replace any PBUF_REF buffers
 * with PBUF_POOL (or PBUF_RAM) pbufs, each taking a copy of
 * the referenced data.
 *
 * @note You MUST explicitly use p = pbuf_take(p);
 * The pbuf you give as argument, may have been replaced
 * by a (differently located) copy through pbuf_take()!
 *
 * @note Any replaced pbufs will be freed through pbuf_free().
 * This may deallocate them if they become no longer referenced.
 *
 * @param p Head of pbuf chain to process
 *
 * @return Pointer to head of pbuf chain
 */
struct pbuf *pbuf_take(struct pbuf *p)
{
        struct pbuf *q , *prev, *head;
        LWIP_ASSERT("pbuf_take: p != NULL\n", p != NULL);
        LWIP_DEBUGF(PBUF_DEBUG | DBG_TRACE | 3, ("pbuf_take(%x)\n", (unsigned int)p));

        prev = NULL;
        head = p;
        /* iterate through pbuf chain */
        do
        {
                /* pbuf is of type PBUF_REF? */
                if (p->flags == PBUF_FLAG_REF) {
                        LWIP_DEBUGF(PBUF_DEBUG | DBG_TRACE, ("pbuf_take: encountered PBUF_REF %x\n", (unsigned int)p));
                        /* allocate a pbuf (w/ payload) fully in RAM */
                        /* PBUF_POOL buffers are faster if we can use them */
#if 0                        
                        if (p->len <= PBUF_POOL_BUFSIZE) {
                                q = pbuf_alloc(PBUF_RAW, p->len, PBUF_POOL);
                                if (q == NULL) {
                                        LWIP_DEBUGF(PBUF_DEBUG | DBG_TRACE | 2, ("pbuf_take: Could not allocate PBUF_POOL\n"));
                                }
                        } else {
                                /* no replacement pbuf yet */
                                q = NULL;
                                LWIP_DEBUGF(PBUF_DEBUG | DBG_TRACE | 2, ("pbuf_take: PBUF_POOL too small to replace PBUF_REF\n"));
                        }
#else
                        q = NULL; /* I hate PBUF_POOL, performance sucks */
#endif                        
                        /* no (large enough) PBUF_POOL was available? retry with PBUF_RAM */
                        if (q == NULL) {
                                q = pbuf_alloc(PBUF_RAW, p->len, PBUF_RAM);
                                if (q == NULL) {
                                        LWIP_DEBUGF(PBUF_DEBUG | DBG_TRACE | 2, ("pbuf_take: Could not allocate PBUF_RAM\n"));
                                }
                        }
                        /* replacement pbuf could be allocated? */
                        if (q != NULL) {
                                /* copy p to q */
                                /* copy successor */
                                q->next = p->next;
                                /* remove linkage from original pbuf */
                                p->next = NULL;
                                /* remove linkage to original pbuf */
                                if (prev != NULL) {
                                        /* prev->next == p at this point */
                                        LWIP_ASSERT("prev->next == p", prev->next == p);
                                        /* break chain and insert new pbuf instead */
                                        prev->next = q;
                                        /* prev == NULL, so we replaced the head pbuf of the chain */
                                } else {
                                        head = q;
                                }
                                /* copy pbuf payload */
                                memcpy(q->payload, p->payload, p->len);
                                q->tot_len = p->tot_len;
                                q->len = p->len;
                                /* in case p was the first pbuf, it is no longer refered to by
                                 * our caller, as the caller MUST do p = pbuf_take(p);
                                 * in case p was not the first pbuf, it is no longer refered to
                                 * by prev. we can safely free the pbuf here.
                                 * (note that we have set p->next to NULL already so that
                                 * we will not free the rest of the chain by accident.)
                                 */
                                pbuf_free(p);
                                /* do not copy ref, since someone else might be using the old buffer */
                                LWIP_DEBUGF(PBUF_DEBUG, ("pbuf_take: replaced PBUF_REF %x with %x\n", (unsigned int)p, (unsigned int)q));
                                p = q;
                        } else {
                                /* deallocate chain */
                                pbuf_free(head);
                                LWIP_DEBUGF(PBUF_DEBUG | 2, ("pbuf_take: failed to allocate replacement pbuf for %x\n", (unsigned int)p));
                                return NULL;
                        }
                        /* p->flags != PBUF_FLAG_REF */
                } else {
                        LWIP_DEBUGF(PBUF_DEBUG | DBG_TRACE | 1, ("pbuf_take: skipping pbuf not of type PBUF_REF\n"));
                }
                /* remember this pbuf */
                prev = p;
                /* proceed to next pbuf in original chain */
                p = p->next;
        } while (p);
        LWIP_DEBUGF(PBUF_DEBUG | DBG_TRACE | 1, ("pbuf_take: end of chain reached.\n"));

        return head;
}

/**
 * Dechains the first pbuf from its succeeding pbufs in the chain.
 *
 * Makes p->tot_len field equal to p->len.
 * @param p pbuf to dechain
 * @return remainder of the pbuf chain, or NULL if it was de-allocated.
 * @note May not be called on a packet queue.
 */
struct pbuf *pbuf_dechain(struct pbuf *p)
{
        struct pbuf *q;
        u8_t tail_gone = 1;
        /* tail */
        q = p->next;
        /* pbuf has successor in chain? */
        if (q != NULL)
        {
                /* assert tot_len invariant: (p->tot_len == p->len + (p->next? p->next->tot_len: 0) */
                LWIP_ASSERT("p->tot_len == p->len + q->tot_len", q->tot_len == p->tot_len - p->len);
                /* enforce invariant if assertion is disabled */
                q->tot_len = p->tot_len - p->len;
                /* decouple pbuf from remainder */
                p->next = NULL;
                /* total length of pbuf p is its own length only */
                p->tot_len = p->len;
                /* q is no longer referenced by p, free it */
                LWIP_DEBUGF(PBUF_DEBUG | DBG_STATE, ("pbuf_dechain: unreferencing %x\n", (unsigned int)q));
                tail_gone = pbuf_free(q);
                if (tail_gone > 0) {
                        LWIP_DEBUGF(PBUF_DEBUG | DBG_STATE,
                                    ("pbuf_dechain: deallocated %x (as it is no longer referenced)\n", (unsigned int)q));
                }
                /* return remaining tail or NULL if deallocated */
        }
        /* assert tot_len invariant: (p->tot_len == p->len + (p->next? p->next->tot_len: 0) */
        LWIP_ASSERT("p->tot_len == p->len", p->tot_len == p->len);
        return (tail_gone > 0? NULL: q);
}
